Remove cargo packaging code in favor of `cargo package` command

[jwric]

Following the stabilization of rust-lang/cargo#10948, the cargo package command will be able to generate crate archives for multiple local crates at once. It would be a good idea to try to make use of this feature instead of relying on the code from cargo we have ported to our codebase.

[ThierryCantin-Demers]

We should not support git dependencies for now. We should only support public crates (on crates.io) and local crates (in the same workspace as the user's base crate)